/*
 * Copyright 2002-2015 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.aop.aspectj;

import java.io.Serializable;

import org.springframework.core.Ordered;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * Implementation of {@link AspectInstanceFactory} that is backed by a
 * specified singleton object, returning the same instance for every
 * {@link #getAspectInstance()} call.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see SimpleAspectInstanceFactory
 * @since 2.0
 */
@SuppressWarnings("serial")
public class SingletonAspectInstanceFactory implements AspectInstanceFactory, Serializable {

    private final Object aspectInstance;


    /**
     * Create a new SingletonAspectInstanceFactory for the given aspect instance.
     *
     * @param aspectInstance the singleton aspect instance
     */
    public SingletonAspectInstanceFactory(Object aspectInstance) {
        Assert.notNull(aspectInstance, "Aspect instance must not be null");
        this.aspectInstance = aspectInstance;
    }


    @Override
    public final Object getAspectInstance() {
        return this.aspectInstance;
    }

    @Override
    @Nullable
    public ClassLoader getAspectClassLoader() {
        return this.aspectInstance.getClass().getClassLoader();
    }

    /**
     * Determine the order for this factory's aspect instance,
     * either an instance-specific order expressed through implementing
     * the {@link org.springframework.core.Ordered} interface,
     * or a fallback order.
     *
     * @see org.springframework.core.Ordered
     * @see #getOrderForAspectClass
     */
    @Override
    public int getOrder() {
        if (this.aspectInstance instanceof Ordered) {
            return ((Ordered) this.aspectInstance).getOrder();
        }
        return getOrderForAspectClass(this.aspectInstance.getClass());
    }

    /**
     * Determine a fallback order for the case that the aspect instance
     * does not express an instance-specific order through implementing
     * the {@link org.springframework.core.Ordered} interface.
     * <p>The default implementation simply returns {@code Ordered.LOWEST_PRECEDENCE}.
     *
     * @param aspectClass the aspect class
     */
    protected int getOrderForAspectClass(Class<?> aspectClass) {
        return Ordered.LOWEST_PRECEDENCE;
    }

}
